WDXS32 PGTW 141500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21S (GEZANI) WARNING NR 
014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.9S 36.6E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 297 NM SOUTHWEST OF EUROPA ISLAND
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 21S (GEZANI) AS IT IS CURRENTLY TRANSITING SOUTHEASTWARD
AND AWAY FROM THE COAST OF MOZAMBIQUE. THE SYSTEM HAS WEAKENED
SIGNIFICANTLY AS OBSERVED BY A NOW FULLY FILLED EYE FEATURE REPLACED 
BY A POORLY DEVELOPED CENTRAL DENSE OVERCAST (CDO). SIGNIFICANT
AMOUNT OF DRY AIR CAN BE SEEN IN THE EIR IMAGERY SURROUNDING THE
SYSTEM AND BEGINNING TO ENTER THE CORE OF THE VORTEX. AS SUCH, THE 
ENVIRONMENT IS BECOMING INCREASINGLY LESS FAVORABLE, DESPITE REMAINING 
FAIRLY WARM (27-28 C) SEA SURFACE TEMPERATURES (SST) AND LOW (0-5 KTS) 
VERTICAL WIND SHEAR (VWS). THE INITIAL POSITION IS PLACED WITH MEDIUM 
CONFIDENCE BASED ON THE EXTRAPOLATION OF A MICROWAVE EYE SEEN IN THE 
141056Z GPM GMI COLOR 37 GHZ PASS. THE INITIAL INTENSITY OF 90 KTS IS 
ALSO ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE SUITE OF OBJECTIVE 
AIDS AND DVORAK AGENCY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR)
CENTERED TO THE SOUTHEAST, INTERRUPTED BY A PASSING LONG-WAVE
BAROCLINIC TROUGH TO THE SOUTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   DEMS: T5.5 - 102 KTS
   CIMSS ADT: 90 KTS AT 141130Z
   CIMSS AIDT: 95 KTS AT 141130Z
   CIMSS D-MINT: 87 KTS AT 141057Z
   CIMSS D-PRINT: 84 KTS AT 141200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 0-5 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK RADIAL
   OTHER FACTORS: DRY AIR SURROUNDING THE SYSTEM

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC 21S IS BEGINNING TO INTERACT WITH AN 
AMPLIFYING, DEEP-LAYER, BAROCLINIC TROUGH PROPAGATING FROM THE
SOUTHWEST. THIS NEWLY ESTABLISHED STEERING REGIME WILL GOVERN THE 
TRAJECTORY OF THE SYSTEM FOR THE NEXT 24-36 HOURS. AFTER THAT, THE 
BAROCLINIC TROUGH IS EXPECTED TO PASS EASTWARD, WHILE LEAVING TC 21S 
BEHIND. DURING THAT TIME, THE PREVIOUSLY DOMINANT STEERING STR LOCATED 
TO THE EAST OF MADAGASCAR WILL BUILD AND REGAIN STEERING CONTROL FOR 
TC GEZANI YET AGAIN. DURING THAT PHASE, THE ENVIRONMENT IS EXPECTED TO 
BECOME INCREASINGLY MORE HOSTILE, WITH VWS REACHING 30+ KTS, SSTS 
BECOMING COOLER DUE TO UPWELLING AND CONTINUOUS DRY AIR INTRUSION. AS 
THE SYSTEM BECOMES MORE SHALLOW, IT IS FORECAST TO BEGIN ITS 
EXTRATROPICAL TRANSITION (ETT) AROUND 72, WHICH IS EXPECTED TO 
COMPLETE BY TAU 96. IN REGARD TO INTENSITY, WEAKENING IS PREDICTED 
THROUGHOUT THE CURRENT FORECAST, WITH A BRIEF PERIOD OF STEADYING, 
AROUND TAUS 36 AND 48, DUE TO TEMPORARY DECREASE IN VWS.

MODEL DISCUSSION: OVERALL TRACK FORECAST CONFIDENCE IS IMPROVING,
BUT STILL CURRENTLY ASSESSED AS LOW, PRIMARILY DUE TO SIGNIFICANT
UNCERTAINTY ASSOCIATED WITH THE TIMELINE AND SHARPNESS OF THE
RECURVATURE IN THE TRACK, BEGINNING AT TAU 24. THE DETERMINISTIC ECMWF 
AND ECMWF ENSEMBLE SUITE ARE ON ONE SIDE OF THE GUIDANCE ENVELOPE 
SUGGESTING A SHARP NORTHWARD TRACK TURN BEGINNING AT TAU 24, WITH THE 
SYSTEM REACHING AS FAR AS 22 DEGREES SOUTH, JUST BEFORE IT GETS PICKED 
UP BY THE STEERING RIDGE AND IS DRIVEN SOUTHWARD.  THE REMAINDER OF 
THE MULTI-MODEL CONSENSUS MEMBERS DEPICT A SLOWER AND A MORE GRADUAL 
TURN TOWARDS MADAGASCAR BETWEEN TAU 24 AND 36, FOLLOWED BY A RAPID 
CHANGE IN STEERING PATTERN, RESULTING IN A POLEWARD TURN IMMEDIATELY 
AFTERWARDS. THE INTENSITY PREDICTION IS ASSESSED WITH MEDIUM 
CONFIDENCE, AS THE GUIDANCE SUITE EXHIBITS A HIGHER DEGREE OF 
CONVERGENCE. ALTHOUGH A SPREAD OF 25-35 KTS IS STILL EVIDENT, ALL 
MEMBERS ARE UNIFIED IN PROJECTING A STEADY ATTENUATION TREND AT A 
MODERATE RATE. THE JTWC INTENSITY FORECAST IS ALIGNED CLOSELY WITH THE 
MULTI-MODEL CONSENSUS.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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